This invention relates generally to networks of interconnected computers and, more particularly, to techniques for routing messages or data packets from one node to another in a xe2x80x9clocallyxe2x80x9d located intranet. The nature of the invention first requires a few definitions by way of background. Relatively small networks, perhaps of up to a few hundred nodes and typically located in a single building or group of buildings, are referred to as local area networks (LANs). When the nodes are further apart, the terms xe2x80x9cwide area networkxe2x80x9d or xe2x80x9cmetropolitan area networkxe2x80x9d are sometimes used, but the distinction is one of degree and the definitions sometimes overlap. LANs are typically interconnected through switching nodes called bridges and routers, to form a large xe2x80x9cinternetxe2x80x9d of interconnected computer nodes.
The internet with which most computer users are familiar is referred to as the Internet. Interconnection of nodes on the Internet, and the transmission of data between them, is governed by a set of protocols defined by the Internet community and called the Internet protocol (IP) suite, or sometimes the TCP/IP suite. (TCP is xe2x80x9ctransmission control protocol.xe2x80x9d)
The term xe2x80x9cintranetxe2x80x9d is used to refer to a localized portion of the Internet that is confined to a specific enterprise, such as a corporation or a governmental, educational or military organization. An intranet typically includes multiple interconnected LANs and may extend over a large geographical area. Use of the term intranet implies a commonality of interest among the users of the nodes in the intranet, and usually a commonality of ownership and control as well.
Multiple intranets are interconnected in the Internet by high-bandwidth xe2x80x9cbackbonexe2x80x9d communication links, such as leased lines. Individual LANs in the Internet may also have relatively high bandwidth, which is a measure of their data carrying capacity. There are some situations, however, in which the bandwidth of an intranet is severely strained by the traffic of data packets and administrative messages being transmitted. This is especially true for intranets including increasingly popular wireless and mobile communications nodes. In wireless networks, the bandwidth is inherently limited in comparison to networks that use coaxial cables or optical fibers as a transmission medium.
In the Internet, messages and data are addressed to users by user name, i.e., a name that the user of a network node has selected or has been assigned, and a domain name, which is usually a name, nickname or abbreviation selected by an organization with which the user is affiliated in some way, as an employee or subscriber, for example. One of the main problems that must be solved in inter-networks is to determine the path that data packets should traverse to reach end destinations. This problem is usually addressed by devices known as routers, or by routing software in host platforms. Routers make decisions regarding packet forwarding based on numeric addresses, rather than symbolic names. The host computer that originates the packet (the xe2x80x9csourcexe2x80x9d computer) has the responsibility of determining the numeric address (xe2x80x9cIP addressxe2x80x9d) of the destination, generally by using services provided by special network nodes referred to as xe2x80x9cname serversxe2x80x9d. After determining the IP address of the destination, the source will send the message, in one or more data packets, to the local router for further processing.
There are a number of options that can be employed by such routers in order to make proper forwarding decisions, but they fall into two main categories: the routers can be pre-programmed with xe2x80x9cstaticxe2x80x9d routing information, or they can run a dynamic routing protocol. In the latter case, the routers constantly exchange administrative data packets throughout the network; these administrative data packets contain the information required for the routers to find paths to the destinations of interest. The first approach (xe2x80x9cstatic routingxe2x80x9d), has the advantage of not requiring continual usage of network bandwidth for the exchange of such administrative information, but has two main disadvantages: First, it complicates the network planning process, since all possible routing paths must be anticipated and included in the routing tables of each router in the network; Second, it does not allow adaptations to failed communication links, or to hosts that join the network at arbitrary locations after the planning process has been completed. This second shortcoming may be less important in an environment where hosts do not move and the communication media are extremely reliable, but is not suitable for a wireless network with mobile communication nodes.
The second approach (xe2x80x9cdynamic routingxe2x80x9d) overcomes the disadvantages of the static approach, but at the cost of the communications load burden on the communications network of the continuous exchange of administrative data packets containing routing information between each of the routers. In most applications of the Internet, the additional bandwidth overhead imposed by these messages does not degrade network performance significantly. Even in intranets in which bandwidth has become limited for one reason or another, the overhead is tolerated because it serves a necessary function, and because connection to the Internet requires adherence to TCP/IP standards.
An intranet with an inherently low bandwidth, however, such as an intranet that includes wireless LANs, is more significantly affected by the overhead of these administrative messages used for path finding and routing purposes. Therefore, there is a need for a method of message routing within an intranet that can operate without the bandwidth overhead usually associated with the Internet, but which still allows connection to the Internet in conformance with TCP/IP standards. The present invention satisfies this need.
The present invention resides in a method for establishing a communication path between two nodes of an intranet without using the conventional path finding and routing techniques associated with networks. Briefly, and in general terms, the method of the invention comprises the steps of: using an auxiliary communication channel to establish switched virtual circuit between a first router associated with a first host and a second router associated with a second host; transmitting data packets in both directions over the switched virtual circuit; and deactivating the switched virtual circuit when packet transmission activity has ceased for a selected time. Before establishing the switched virtual circuit, the method xe2x80x9cfindsxe2x80x9d the second router associated with the second or xe2x80x9cdestinationxe2x80x9d host computer.
More specifically, the method may be defined as including the steps of: transmitting from a first host in an intranet, a first data packet addressed to a second host in the same intranet; receiving the first data packet at a first router near the first host; broadcasting from the first router, over an auxiliary communication channel, a request message identifying the second host; receiving the request message at a second router, which recognizes the second host identified in the request; transmitting over the auxiliary communication channel a response to the request message from the second router to the first router, providing a complete address for the second host; establishing in the first router, upon receiving the response to the request message, a switched virtual circuit between the first and second routers; transmitting the first data packet from the first router to the second router over the switched virtual circuit; and transmitting the first data packet from the second router to the second host, to complete delivery of the first data packet.
The method may further comprise the steps of: retrieving the address of the first host from the first data packet upon its arrival at the second router; and using the address of the first host in the second router, to establish a return path for data packets to be transmitted from the second host to the first host. When the return path has been established, the method further includes transmitting second and additional data packets from the second host to the first host over the switched virtual circuit, and transmitting other additional data packets from the first host to the second host over the switched virtual circuit.
For termination of transmission over the switched virtual circuit, the method also includes the steps of sensing in one of the first and second routers that there has not been any transmission of data packets over the switched virtual circuit for some selected time interval; and deactivating the switched virtual when the sensing step determines that the selected time of inactivity has elapsed.
In one disclosed embodiment of the invention, the first and second hosts are attached to different networks, neither of which has an auxiliary communication channel, and the step of transmitting a first data packet to the first router includes transmitting the first data packet through a second network to which the first host and the first router are both connected. In addition, the step of transmitting the first data packet from the second router to the second host includes transmitting the first data packet through a third network to which the second host and the second router are both connected, and the subsequent steps of transmitting second and additional data packets include transmitting them through the second and third networks.
It will be appreciated from the foregoing summary that the present invention represents a significant improvement in the field of network communication. In particular, the invention provides a technique for establishing a communication path in a very-low bandwidth intranet, such as a wireless intranet, without sacrificing bandwidth capacity for use by continual administrative messages. Other aspects and advantages of the invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings.